1. Field of the Invention
The present invention relates to the structure of rotary actuator assemblies which provide a dynamic torque input to a test specimen.
2. Description of the Prior Art
Rotary hydraulic actuators are commonly known and are used in testing specimens such as shafts or axles. Typically, the shaft or axle is driven at one end with a motor and is connected at the other end in a suitable manner to the rotary actuator.
The rotary actuator is used to introduce dynamic torque loads or forces into the shaft or axle to simulate the shaft's actual usage in a machine, such as an axle in an automobile. During such simulation testing, the safety and reliability of the axle is determined.
Typically, the rotary hydraulic actuator introduces the dynamic torque loads through a servovalve controlled hydraulic system, with the hydraulic forces being delivered into a rotating hydraulic actuator of the rotary actuator through a hydraulic commutator. A typical construction of such a hydraulic actuator is shown in FIG. 2 of the Petersen patent, U.S. Pat. No. 3,690,168, which is assigned to the same assignee as the present invention. The dynamic torque loads need to be introduced in a consistent manner such that reproducable and statistically sound testing can be performed on the specimen. Consequently, the rotary actuator has to be built in a precise manner.
The rotary hydraulic actuator includes an integral shaft portion that is positioned between the test specimen and the hydraulic commutator. The shaft portion is mounted on a heavy duty bearing to insure true location of the shaft portion at high speeds thereby providing the consistent dynamic torque loads to test specimens while reacting to any side loads. Typically, the heavy duty bearing requires a fluid lubricant (oil) to be applied thereto under pressure. The lubricating oil is normally applied from the outside of the bearing, while seals on the other side of the bearing keep the fluid lubricant from escaping and landing on rotating parts and splashing. The assembly of the shaft portion and bearings along with the seals is an expensive one in trying to produce a durable and precise rotatable bearing support.